Clarify that the two statements about additional joins refer to different things

In the section on Including multiple levels it says "This does not mean you will get redundant joins". Then just below the example it says "Since version 3.0.0, each Include will cause an additional JOIN to be added". It's not clear whether the warning only applies where you are including different entities or whether it applies even when you are including the same entity more than once as in the example

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* ID: bbd36f35-e257-d0ed-8f28-f539ddcb71ec
* Version Independent ID: 093903d5-f7c7-5a78-c0e5-0e2662dcedef
* Content: [Loading Related Data - EF Core](https://docs.microsoft.com/en-us/ef/core/querying/related-data#feedback)
* Content Source: [entity-framework/core/querying/related-data.md](https://github.com/aspnet/EntityFramework.Docs/blob/master/entity-framework/core/querying/related-data.md)
* Product: **entity-framework**
* Technology: **entity-framework-core**
* GitHub Login: @rowanmiller
* Microsoft Alias: **avickers**